Lighting device

ABSTRACT

A lighting device for elongate transparent scale plates, wherein a mirror is made up of a parabolic curved wall and flat walls attached to the upper and lower sides of said parabolic curved wall each at an angle thereto, and a light source is mounted on said parabolic curved wall, whereby the elongate transparent scale plate is uniformly lighted.

United States Patent Hirota Nov. 13, 1973 LIGHTING DEVICE 2,562,498 71951 Leboffe 240/8.16 1,668,515 5/1928 Lewellen 240/8.l6 [75] Japan1,302,924 1919 l-lollnagel et a1. 240 4135 E [73] Assignee: Kyowa DenkiKagaku Kabushiki SAGE 5? K h T k c otz....

0 Japan 1,950,330 3 1934 Thrall 240 4135 A [22] Filed: Dec. 13,1971

Appl. N0.2 207,006

Foreign Application Priority Data Dec. 30, 1970 Japan /129364 US. Cl240/2.l, 240/8.16, 240/4135 A, 240/4135 E, 116/1244 Int. Cl. G0ld 11/28Field of Search 1l6/124.1, 124.4, 116/116, 240/4135, 41.35 A, 41.35 B,41.35 E, 2.1, 7.1 C, 8.16, 8.2,,8.22, 8.24, 41.5

References Cited UNITED STATES PATENTS Hammond 240/8.16

Primary ExaminerRichard M. Sheer AttorneyJohn Lezdey et a1.

[57] ABSTRACT A lighting device for elongate transparent scale plates,wherein a mirror is made up of a parabolic curved wall and flat wallsattached to the upper and lower sides of said parabolic curved wall eachat an angle thereto, and a light source is mounted on said paraboliccurved wall, whereby the elongate transparent scale plate is uniformlylighted.

1 Claim, 5 Drawing Figures PAIENIEUNM 13 ms 3772.509

'FIG.I '9

PRIOR ART FIG.2

INVENTOR KRSHI H H OTA BY? 2 ATTORN LIGHTING DEVICE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a lightingdevice and more particularly to a lighting device for elongatetransparent scale plates such, for example, as frequency calibrationscales of radio receivers.

2. Description of the Prior Art Most of the frequency calibration scalesprovided on the cabinets of radio receivers are of the type consistingusually of an elongate transparent plate with scale marks engravedtherein and adapted to be lighted by a light permeating therethrough.Some of the lighting devices heretofore used for lighting such scalescomprise two or more miniature electric bulbs located behind theelongate transparent scale 'plate mounted over a slot formed in a paneland a curved mirror disposed behind said electric bulbs. However, suchlighting devices have the disadvantage that the scale plate is notuniformly lighted and the beams of light emanating upwardly anddownwardly from the electric bulbs dissipate without lighting the scaleplate, so that the loss of light is great and hence the scale plate isnot lighted sufficiently.

Some other lighting devices comprise miniature electric bulbsrespectively disposed adjacent the side faces of a transparent scaleplate which has a relatively large thickness and is mounted on a panel,whereby the scale plate is lighted by the light of said electric bulbspenetrating thereinto from the side faces thereof. In such lightingdevices, the luminous intensity of the light substantially decreasedduring passage of the light through the scale plate and the beams oflight emanating upwardly, downwardly, leftwardly, rightwardly andbackwardly from the electric bulbs are all dissipated, the beams oflight emanating forwardly only being utilized for the lighting purpose,so that the lighting efficiency of the device is very low and the scaleplate is not lighted brightly. In addition, since the lights of theminiature electric bulbs disposed on both sides of the scale plate aredirectly visible through the scale plate mounting slot formed in thepanel, the appearance of the scale plate is spoiled.

SUMMARY OF THE INVENTION According to the lighting device of the presentinvention, every portion of an elongate transparent scale plate can beuniformly lighted from the backside thereof and all of the beams oflight emanating in all directions from a miniature electric bulb isreflected to effectively light the scale plate. Therefore, the scaleplate is lighted very brightly, and the number of the miniature electricbulbs required can be reduced to half of that required in theconventional lighting devices and hence the power consumption isreduced, providing for the use of a small capacity transformer.

Furthermore, by coupling a plastic elongate scale plate with a plasticelongate mirror by means of a bolt extending through a slot formed in apanel, the bulging of the scale plate at the central portion thereof dueto thermal expansion of said scale plate can be avoided because, evenwhen the scale plate is subjected to thermal expansion or contraction,the mirror is expanded or contracted to the same degree as said scaleplate.

The present invention consists in a lighting device of the typecomprising miniature electric bulbs for lighting elongate transparentscale plates, such as the frequency calibration scales of radioreceivers, by the beams of light emanating from said bulbs, which iscapable of lighting uniformly every portion of the scale plate with aminimum number of electric bulbs. Namely, according to the presentinvention there is provided a lighting device comprising mirror meansconsisting ofa plastic body open at the front and having an elongatedvertical back wall of a parabolic shape in cross section and upper andlower flat walls extending forwardly and outwardly relative to eachother, and having the inner surface thereof plated with a glossyplating; and a miniature electric bulb provided on said back wall, formounting on a panel formed with a slot therein and having the oppositeside of said mirror means mounted at locations adjacent the oppositeends of said slot, and a transparent scale plate mounted over the frontface of said slot.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of aconventional lighting device;

FIG. 2 is a perspective view of another type of conventional' lightingdevice;

FIG. 3 is a lateral cross-sectional view of the lighting deviceaccording to the present invention;

FIG. 4 is a vertical cross-sectional view of the lighting device of theinvention; and

FIG. 5 is an enlarged cross-sectional view showing the mounting portionsof the lighting device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there isshown one type of conventional lighting device. In this lighting device,two miniature electric bulbs l3, 14 are disposed behind an elongatetransparent scale plate 12 mounted in a slot formed in a panel 11, andfurther a curved plate-like mirror 15 is disposed behind said bulbs.With such a lighting device, the scale plate 12 is not uniformly lightedand the beams of light emanating upwardly and downwardly from the bulbs13, 14 dissipate without lighting the scale plate 12 at all. Therefore,the loss of light is great and the scale plate 12 is dark.

In another type of conventional lighting device shown in FIG. 2,miniature electric bulbs l8, 19 are provided each adjacent each sideface of a relatively thick transparent scale plate 17 mounted on a panel16. The beams of light emanating from the bulbs 18, 19 penetrate intothe scale plate 17 from the opposite side faces thereof, therebylighting said scale plate. However, the luminous intensity of the lightsubstantially decreases during passage of the light through the scaleplate 17 and moreover the beams of light emanating upwardly, downwardly,leftwardly, rightwardly and backwardly from the bulbs l8, 19 alldissipate wastefully and the beams of light emanating forwardly only areutilized for lighting. Therefore, the lighting efficiency is very poorand the scale plate 17 is dark. In addition, since the lights of thebulbs l8, 19 are visible directly through the slot formed in the panel16, the appearance of the scale plate is spoiled.

Now, the lighting device of the present invention will be described withreference to FIGS. 3 to 5. According to the invention, a mirror A openat the forward end and having a vertical back wall 1 curved toward theopposit'e side edges to form a parabolic surface, and an upper wall 2and a lower wall 3 extending forwardly and outwardly relative to eachother, and further having mounting holes 4, 5 formed in the oppositeside edge portions thereof, is made of a plastic material, and a metalis deposited on the inner surface of said mirror to form a reflectingsurface. A miniature electric bulb 7 is mounted at the center of theback wall 1.

The mirror A constructed as described above is mounted on the backsideof a panel 8 in a manner to cover a slot 9 which is formed in said paneland has transparent scale plate 10 mounted thereover from the front sideof the panel. The scale plate may be made of a semi-transparentmaterial.

The beams of light emitted forwardly from the bulb 7 directly light thescale plate 10. The beams of light emitted backwardly reflect on theparabolic surface of the back wall 1 and light the scale plate 10. Thebeams of light emitted upwardly and downwardly reflect on the upper wall2 and the lower wall 3 respectively, and parts thereof light the scaleplate 10, while the other parts thereof again reflect on the lower wall3 and the upper wall 2 respectively. Since the upper wall 2 and thelower wall 3 extend forwardly and outwardly relative to each other, thebeams of light while repeately reflecting on said walls 2, 3, movegradually forwardly and finally impinge upon the scale plate 10 to lightthe same.

As described above, the beams of light emanating from the bulb 7 otherthan those directly lighting the scale plate 10 reach the scale plate 10upon repeatedly reflecting on the back wall 1, the upper wall 2 and thelower wall 3, and finally, all the beams of light emanating from thebulb 7 light the scale plate 10 and the scale plate 10 is lighted verybrightly.

Where the scale plate is mounted on the panel there is an elongateplastic plate, which expands longitudinally when heated by the heatgenerated from a transformer, resistor, a pilot lamp, etc. and as aresult is subjected to bending with the central portion thereof bulging,since the scale plate is fixed at the opposite end.

In order to eliminate such undesirable phenomenon,

a mounting flange on one side of the mirror A is formed with aprojection 6 which extends forwardly outwardly through a mounting hole21 formed in the panel 8 and contacts the scale plate 10. The mountinghole 21 has a space larger than the space occupied by the projection 6.The mirror and the scale plate are secured to each other by means of ascrew 20, but, as seen, the panel is not secured to either one of them.

The scale plate 10 and the mirror A which are made of plastic materialshave substantially the same coefficient of expansion and coefficient ofcontraction. In addition, the projection 6 at which one side of themirror A is coupled with the scale plate 10 by means of the screw 20, isloosely received in the mounting hole 21. Therefore, the scale plate 10and the mirror A expand or contract integrally with each other and thebending of the scale plate 10 due to thermal expansion can be avoided.

I claim:

1. A uniformly illuminated scale plate device adapted to be mounted on apanel having an elongated slot therein and holes therethrough adjacentthe ends of the slot, comprising a plastic mirror means having anelongated rear wall with a parabolic longitudinal cross sectionterminating, when mounted, adjacent the ends of the slot in the paneland upper and lower substantially flat walls extending from the upperand lower edges of the rear wall upwardly and toward the longitudinalsides of the slot in the panel, an elongated non-opaque, plastic scaleplate marginally larger than the slot in the panel, means for securingthe ends of said plastic mirror means to the ends of said elongatedplastic scale plate through the holes in the panel, said securing meansbeing smaller than at least one of the holes through the panel adjacentthe ends of the slot to permit, when heated, thermal expansion of saidplastic mirror means and said plastic scale plate to prevent bending orbuckling, the marginal edges around the slot in the panel being, whenmounted, disposed between said mirror means and said scale plate, and asource of illumination mounted on said mirror means.

1. A uniformly illuminated scale plate device adapted to be mounted on apanel having an elongated slot therein and holes therethrough adjacentthe ends of the slot, comprising a plastic mirror means having anelongated rear wall with a parabolic longitudinal cross sectionterminating, when mounted, adjacent the ends of the slot in the paneland upper and lower substantially flat walls extending from the upperand lower edges of the rear wall upwardly and toward the longitudinalsides of the slot in the panel, an elongated non-opaque, plastic scaleplate marginally larger than the slot in the panel, means for securingthe ends of said plastic mirror means to the ends of said elongatedplastic scale plate through the holes in the panel, said securing meansbeing smaller than at least one of the holes through the panel adjacentthe ends of the slot to permit, when heated, thermal expansion of saidplastic mirror means and said plastic scale plate to prevent bending orbuckling, the marginal edges around the slot in the panel being, whenmounted, disposed between said mirror means and said scale plate, and asource of illumination mounted on said mirror means.